HAL-Université de Bretagne Occidentale
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Enhancing the Thermal Performance of Solar Air Heaters Using Heat Storage Medium: An Experimental Study With Energy, Exergy, and Economic Approach
No full textInternational audienceAbstract A solar air heater (SAH) is a simple device that collects solar radiation and transfers it to the processed air generally used in several thermal engineering applications such as space and industrial process heating and food drying, but its utilization is only during sunny hours. Among the methods of ameliorating its employing to heat air during the off-sunshine period is through the addition of heat storage medium inside the SAH for storing the sun's radiation as thermal energy. The main objective of this experimental study is to predict the effect of the heat storage medium on the thermal performance of SAH. To achieve this goal, three different configurations of SAHs were designed and constructed in the Laboratory of Electro–Mechanic Systems, namely, traditional SAH with natural circulation (T-SAH), SAH with a centrifugal air blower (F-SAH), and SAH with a centrifugal air blower and coupled with an internal heat storage medium (FS-SAH). They were tested and compared under the same ambient conditions of Sfax, central-eastern Tunisia. Experimental results showed that the T-SAH gives higher temperatures than the F-SAH and FS-SAH during the period from 8 a.m. to 3 p.m. From 3 p.m. to 7 p.m., the temperatures of FS-SAH are the highest when compared with the other two SAHs. Through this period, the thermal energy per unit time obtained by FS-SAH, F-SAH, and T-SAH is 2.15 kW, 0.23 kW, and 0.22 kW, respectively. Due to the use of salt water as a heat storage medium, the thermal energy per unit time of FS-SAH is enhanced by 1.92 kW (corresponding to 89.3%) and 1.93 kW (corresponding to 89.77%) higher than the F-SAH and T-SAH, respectively. The FS-SAH offers higher thermal and exergy efficiency as compared to the T-SAH and F-SAH during the same period. The economic evaluation showed that the money saved by FS-SAH is 96% and 89.51% higher than the T-SAH and F-SAH, respectively. Therefore, the employ of salt water as a heat storage medium is a positive attempt to enhance the thermal performance of SAHs during the off-sunshine period of this experimental testing
A space-time hybrid parareal method for kinetic equations in the diffusive scaling
No full textInternational audienceWe present a novel multiscale numerical approach that combines parallel-intime computation with hybrid domain adaptation for linear collisional kinetic equations in the diffusive regime. The method addresses the computational challenges of kinetic simulations by integrating two complementary strategies: a parareal temporal parallelization method and a dynamic spatial domain adaptation based on perturbative analysis. The parallel in time approach employs a coarse fluid solver for efficient temporal propagation coupled with a fine, spatially-hybridized, kinetic solver for accurate resolution. Domain adaptation is governed by two criteria: one measuring the deviation from local velocity equilibrium, and another based on macroscopic quantities available throughout the computational domain. An asymptotic preserving micro-macro decomposition framework handles the stiffness of the original problem. This fully hybrid methodology significantly reduces computational costs compared to full kinetic approaches by exploiting the lower dimensionality of asymptotic fluid models while maintaining accuracy through selective kinetic resolution. The method demonstrates substantial speedup capabilities and efficiency gains across various kinetic regimes
Élaboration de Métriques pour l’Évaluation du Bruit Propre des Microphones Ambisoniques
No full textElectroacoustique : session générale; GTEA - Transducteurs et ÉlectroacoustiqueNational audienceLe bruit propre constitue un critère fondamental pour la caractérisation des microphones, car il détermine leur rapport signal sur bruit (SNR) et, par conséquent, leur dynamique. Ce bruit est intrinsèquement lié aux propriétés physico-chimiques des matériaux utilisés et à leurs interactions avec les composants électroniques du microphone. Par commodité, il est généralement évalué en fonction de la sensibilité du capteur et exprimé en termes de pression acoustique équivalente. Dans le contexte des antennes microphoniques, chaque capsule contribue au bruit propre global, en fonction des traitements audio appliqués et des spécificités du rendu souhaité. Le cas particulier du rendu binaural, à partir d’un microphone ambisonique, illustre bien cette problématique, car il existe de multiples approches d’encodage et de décodage des signaux. Ces choix techniques influencent directement la qualité finale du rendu audio. À ce jour, aucune méthode consensuelle n’existe pour évaluer le bruit propre de ce type de capteur. Les fabricants se limitent généralement à fournir la valeur correspondant à une capsule individuelle de l’antenne. Ce document a pour objectif de proposer et de comparer plusieurs métriques afin de fournir des outils pratiques permettant d’évaluer et de comparer les performances des équipements matériels et les méthodologies de traitement. En proposant des moyens objectifs de comparaison, cette étude vise à guider les utilisateurs de technologies ambisoniques dans l’optimisation de leurs choix en matière de matériel et de traitement, pour répondre aux exigences spécifiques de leurs applications
Importance du respect de la directivité de la voix lors de sa reproduction dans les cas statiques et dynamiques
No full textDirectivité de la voix et des instruments de musique; GSAM - Acoustique Musicale: GAP - Voix et ParoleNational audienceDans la présente étude, deux « sources vocales » ont été enregistrées (chacune dans deux environnements réverbérants différents) sur une tête artificielle. Ces sources étaient i)un véritable locuteur humain, ii) un haut-parleur mobile sur 3 axes reproduisant le même contenu vocal et les mêmes mouvements que le locuteur humain. Les deux sources présentaient donc les mêmes mouvements, mais des directivités intrinsèques différentes (directivité d’une voix humaine vs directivité d’un haut-parleur). Les enregistrements effectués sur la tête artificielle ont ensuite été écoutés par des auditeurs chargés de les évaluer en termes de plausibilité et de timbre. L'objectif de ces évaluations était de déterminer si le respect de la directivité d'une source sonore (ici une voix humaine) est un élément important lors de la reproduction de celle-ci, selon qu’elle soit statique ou en mouvement
Humpback whales' aversive responses to predator sounds playbacks on their breeding grounds
No full textAcoustique sous-marine et navale, bioacoustique en milieu marin; GAPSUS - Acoustique Physique, Sous-Marine et Ultra-Sonore: GVB - Vibro acoustique et Contrôle du Bruit: GBIO - BioacoustiqueNational audienceAnimal anti-predatory responses provide a valuable yardstick for measuring how they react to perceived high levels of biological threat. In cetaceans, such responses are particularly relevant for assessing the biological significance and severity of their reactions to other disturbances, such as anthropogenic noise. Behavioural responses to perceived threats vary across species and are influenced by social contexts. Previous studies have investigated the anti- predator responses of humpback whales in feeding grounds. In this study, we examine the anti-predator behaviors of humpback whales in their breeding grounds, focusing on mother-calf pairs, which are either alone or accompanied by one male escort. During August 2023 and August 2024 in the Sainte-Marie Channel breeding ground (Madagascar), we conducted playback experiments using unfamiliar mammal-eating killer whale sounds to simulate an immediate predation risk. Behavioral responses were analyzed using data from non-invasive multi-sensor tags attached to the mothers via suction cups, along with visual observations. We compared whale behavior before, during, and after each sound exposure. The results (n=5) indicate that when exposed to the predatory sound playbacks, the mother-calf pairs exhibited a clear avoidance response, moving away from the sound source, either along the canal or toward the coastline. Data from the tagged whales showed an increase in forward speed, a reduction in diving activity (including the number, duration, and dive depth), and synchronized movement with male escorts when present. This avoidance response continued during the post-playback period but ceased shortly and contrasted sharply with the neutral response to control broadband noise. These findings demonstrate that the avoidance anti-predation strategy is conserved in humpback whales on their breeding grounds. The cohesive and synchronized movement of all group members, including the calf staying with its mother and the escort maintaining proximity, suggests the importance of group cohesion in anti-predator strategies, rather than individual protective behaviors
Facial Expressions in Conversational AI: the Hot Trend that Boosts Empathy but Flops on Trust
No full textInternational audienceDynamic facial expressions in AI conversational agents are a rising trend, enhancing emotional engagement and user satisfaction by making interactions feel more personal and engaging. An experimental design comparing two chatbots—one with dynamic expressions and one without—showed that while expressions enhance emotional connection, they fall short in improving trust or advice quality. Absence of expressions fits contexts requiring objectivity and transparency. These findings stress the growing importance of a context-sensitive design in conversational AI, where emotional cues are carefully balanced to match user expectations
Biopsy sampling of red muscle does not affect physiological performances in rainbow trout
No full textInternational audienceMuscular biopsy is a non-lethal muscle sampling technique that allows for the fish to be returned to its natural environment or its tank after sampling. This technique offers the opportunity for the fish farmers and scientific community to carry out assays on very small muscle samples (between 1 and 40 mg) such as lipid composition, trace element and heavy metal levels or muscle energetic metabolism to evaluate, for instance, the health of the fish. The aim of the present study was to determine if a red muscle biopsy affects rainbow trout (Oncorhynchus mykiss) physiological performances (swimming and hypoxia resistances) and their survival. Fish that had a biopsy (n=30) or not (n=30) were subsequently tested for either a hypoxia resistance test (HRT) or a swimming resistance test (SRT) which were conducted 7- and 10-days post-surgery (dps), respectively. Results showed that biopsy had no effect on hypoxia resistance and on swimming parameters (tail beat frequency, sustained and critical swimming speeds, standard and maximal oxygen consumptions). Even if no significant effect was observed between control and biopsy groups on morphometric parameters (body weight variation and condition factors), all the trout lost weight which can be explained by a post-surgery trauma such as local inflammation or human manipulation stress. Furthermore, body weight variation was significantly more important for the 7-dps group compared to the 10-dps group which had the opportunity to eat three more days compared to the 7-dps trout. Corroborated with the principal component analysis, red muscle biopsy can be considered as a relevant approach as it had no effect on whole-animal performance and it did not affect their survival
Increase in ENSO frequency and intensity under 20th and 21st century warming: Insights from CMIP6 large ensembles
No full textInternational audienceFuture changes in El Niño‐Southern Oscillation (ENSO), the dominant mode of global climate variability, remain uncertain. Accordingly, large ensembles—which allow internally‐generated variations to be averaged out—are essential for assessing the response of ENSO to external forcing. In this study, we analyze state‐of‐the‐art large‐ensemble simulations from CMIP6 climate models and show that, in most models, ENSO frequency increases under anthropogenic warming. Two factors drive this frequency increase. First, a shift toward the Eastern Pacific (EP) El Niño pattern—characterized by higher frequencies and greater amplitudes relative to the Central Pacific (CP) pattern. Second, an overall increase in the frequency of both EP and CP variability. These changes scale with the intensity of anthropogenic forcing. Most models also exhibit ENSO strengthening that begins in the century and continues throughout the century. Consequently, the observed intensification of ENSO during the second half of the century could be of anthropogenic origin